That the teen sex guide “Risky Times” that Matt Damon discussed on “The Tonight Show with Jay Leno”— ribbing his pal, Ben Affleck, in the process — was written by Matt’s ex-stepmom, former WBZ medical reporter Jeanne Blake. Blake’s 1991 tome was meant to teach teens about safe sex during the AIDS crisis, and she interviewed six of her stepson’s pals for the book. “Yes, that’s Ben. And all the sex he wasn’t getting,” Damon teased as Leno showed off a black-and-white photo of a gawky Affleck from the book. “There’s some good dirt on Ben in there, I’m sure. I haven’t read it in years. And probably some pretty horrible pictures.”